254 PRACTICAL HISTOLOGY. [XXIL 



With a high power it is easy to observe the structure of the 

 .& 



Epithelium. 



FIG. 245. Diagram of Early 

 Stage of the Development 

 of a Tooth, a. Epithelium 

 of dental ridge on lower 

 jaw ; b. Portion of epithe- 

 lium about to be modified 

 into enamel (enamel organ); 



c. Beginning of germ of den- 

 tine in the tooth papilla ; 



d. Lamination of corium 

 about to form tooth sac. 



FlG. 246. Lower Jaw of Human Foetus at 4th 

 Month, x 40. i. Dental ridge; 2* Stalk of 

 enamel germ ; 3. Enamel organ ; a. Peri- 

 pheral cells ; b. Germ pulp ; c. Cylindrical 

 cells of enamel ; 4. Papilla. 



several parts, and to see the odontoblasts lining what is to be the 



Dental Sac. 



(Outer layer 



] 



(inner lay 



Dentine. ~t 



f Odontoblasts. 

 PapittaA Spherical elements __ 

 v. with blood-vessels. 



Bone of the lower jaw.- 



Peripheral flat^ 



cells. 



Enamel pulp. , 

 Enamel cells. ( or! ' an ' 



Enamel. 



FIG. 247. T.S. Lower Jaw of New-Born Dog, x 40. The dental sac is shown only in the 

 left side. The tissues originating from connective tissue are shown on the left, and 

 those of epithelial origin on the right. 



pulp-cavity. If the latter happen to be partially detached, their 





